On Tue, 04 Jan 2011 17:14:44 -0700, D Yuniskis
wrote:

...

That depends on the actual charger configuration -- hence my
asking if it was a 24V monoblock or a pair of 12V monoblocks.


With the exception of a few vehicles, all military vehicles use a
standardized 24V alternator to charge two 12V batteries connected in
series. The exceptions are some new HMMWVs with the 4L80E transmission
which have a combination 24/12 volt alternator (which is really
expensive, a couple of thousand dollars), needed because the
transmission controller requires 12Volts, and some older military
pickup trucks (based on commercial pickups) that used two 12V
alternators to minimize the modifications needed to the electrical
system to convert them to military voltage standards.

Given that this is the *military*, I am assuming that they
have deep enough pockets to create their own standards
(e.g., 400Hz power).

The military didn't create 400Hz power, IIRC, it is a standard for
aircraft electronics. It is used to keep transformer weights down in
an environment where weight is critical. The military uses 400 Hz for
some ground equipment, but often this equipment is based on airborn
electronics.

As such, if they opted for two 12V
monoblocks in the vehicle, I would assume they would have
also designed a charging system that *treated* them as
two 12V monoblocks and not a "24V battery"

Not sure what you are saying when you use the term 'monoblocks', all
military vehicles use 12V batteries in series. There is never
(excluding the exceptions noted above) a connection to the lower
battery except to the upper battery.

-- since the
added cost of charging them as two monoblocks would easily
be outweighed by the increased "battery" life that obtains
from that since imbalances between cells are a (the?) primary
cause of battery failure (presumably the military wouldn't
want to have to lug around spare batteries if they could make
the ones they had last longer -- esp. in a war zone). Cells
will *try* to equalize with overcharging in short strings
but, as the string gets longer, battery life goes to hell
(since the "good" cells get overstressed trying to "coax"
the bad ones back in line; and, as a cell gets bad, it gets
bad-er!)

Generally speaking you try to keep the battery pairs as matched as
possible, and occasionally you check the charge for each one. If one
is not being charged properly, replace them.


But, I've never peeked under the hood of a military vehicle
so can't tell if:
- 1 monoblock or two

Again, what's a monoblock? A battery? Then yes, all have two 12volt
batteries. Yes, I have a number of military vehicles. And yes, I'm
well famiiliar with the electrical configurations for these setups.

- three terminals to the battery or just two

Standard batteries. In fact, I often use batteries I buy from TSC in
my equipment--they are cheaper and usually have a compatible form
factor. Big trucks (like the 2 1/2 ton truck) use big truck batteries,
but they are still standard batteries.

- is the *entire* system running at 24V (or just parts that
draw higher currents)

Generally everything that can be run on 24 volts runs on 24volts. The
transmission controller on HMMWVs can't, so it runs on 12volts from
the dual voltage system. It is an exception! But all lights,
electronics, etc., are 24 volts on military vehicles--the military
doens't like multiple standards...